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Thursday, January 2, 2014

Walk this way, talk this way, roll in the hay

Teaching anthropology and human evolution involves tearing down stubborn misconceptions and stimulating students to discover and to behold their culturally-limited assumptions objectively.

That's if you're skilled and if you're lucky. OK, let's be honest: that's if you're supernatural.

The job sometimes feels like digging a hole, going deeper and deeper, never having the chance to mold something out of all that dirt, to build upon existing knowledge and insights. To move upward and onward.

Enough preamble though. There's a point today and it's got to do with:

I just finished a semester of Paleoanthropology where my students were asked to answer, "What happened to the Neanderthals?" for their course-long and final projects.

Even a familiarity with Neanderthals from their Intro to Bioanth or their Intro to Archaeology course does not fully prepare all upper-level Paleoanthropology students to consider them in a more advanced scientific framework. In fact, I think that familiarity combined with the claws of pop culture can inhibit them.

Despite hosting an expert to present to my students the many obstacles and issues with identifying extinction and its causes in the fossil record, and despite an admittedly brief but explicit exposure to the cutting edge genetic evidence, some of them still assumed they were charged to find the cause of Neanderthal extinction.

Two of them went so far as to rewrite my question at the top of their final paper as, "Why did the Neanderthals go extinct?" They had no idea that their version of my question contained assumptions. It's got to have a lot to do with the fact that we kicked off the first week of class and their assignment by binge-reading "The Humans Who Went Extinct" by Finlayson. The book does a wonderfully broad treatment of the issues, but I was completely blind to the title's potential to inhibit nuance. If I'd anticipated this I would have discussed extinction much more during the course. [Consider this post, as so many are, an elaborate note to self.]

The trouble, as I see it, is it's unclear whether the Neanderthals went extinct the same way that we consider the Dodo to have gone extinct or the same way that dinosaurs (except birds) did at the end of the Cretaceous, etc.

Of course there aren't any Neanderthals alive now. But there aren't any australopiths alive now either and nobody's talking about australopith extinction. Australopiths begat or, if you'd rather, evolved into Homo. Ardipithecus didn't go extinct either. As of now we think and say that they evolved into (or, e.g., are in an ancestor-descendant relationship with) Australopithecus.

Aside from Neanderthals, Paranthropus is probably the only other hominin taxon that we discuss in terms of extinction. If its phylogenetic position is correct (and there is no dispute that I know of beyond the debate over one or two genera), then it left no living descendants and faded from the fossil record about a million years ago during a time when many other sub-Saharan fauna disappeared too. But these creatures were weird little bipedal apes, not stocky and muscular, big-eyed, big-nosed, ginger-haired, complexly cultured Europeans as the Neanderthals seem to have been. It's obvious to me why we obsess over the demise of the latter and not the former.

Anyway. Point is. I think we're being a bit intellectually reckless assuming Neanderthal "extinction." To me the question of their fate is more fairly posed "What happened to them?" with a strong answer being extinction but with a kind of extinction that needs to be carefully defined.

In order to hold the Neanderthal demise apart as special, as an exclusive story of "extinction," it needs to be shown that other long-dead LSA/UP hominins that we don't call "Neanderthals," but that we might claim as our more direct ancestors, didn't go "extinct" or have no story of extinction to tell. Don't you think?

[Aside: Here's where questions of cultural demise vs. continuity that are being addressed by archaeologists really might help. But again, we face problems because we know from modern examples that culture change does not equal genetic change and culture stasis does not equal genetic stasis.]

Further, and probably more significant here: If Neanderthal "extinction" is the answer then it needs to account for the factoid that 23andMe says I have 2.9% Neanderthal (77th percentile for site users) in my genome which, as a Homo sapiens, is already more than 99% the same as a Neanderthal's.

There are at least 12 people who are more Neanderthal than I am.

I know that's confusing. I read the 23andMe methods paper, which is supposed to be simpler than the published one, but I still don't understand much about how they make the estimate.

Basically, it's about a percentage of SNPs (single nucleotide polymorphisms, a.k.a. mutations) that I share with dead Neanderthals but that so many live Africans (who I'm more closely related to!) do not. Therefore, if the methods are generally good, my genome contains evidence that people in my ancestry mated with Neanderthals. People who do not have these mutations either (a) never had Neanderthal mutations flow into their ancestors' families, or if they did (b) those Neanderthal mutations drifted away before science could capture them from descendents today.

[You only got one mutation from mom and one from dad, the other part of the pair in each parent that you didn't get are dead ends (extinct!) unless your siblings or cousins got them. So a lot of SNPs and other variants disappear regularly and, on the other hand, everybody has new variants compared to their parents thanks to constant mutation.]

Tendrils of my ancestry must have been much more Neanderthal than 2.9%, but those SNPs drifted away over time. In other words, far enough back there had to be at least one hominin with a 100% Neanderthal genome in my ancestry (whatever that means), because that's the only way the genes got to me in the first place...but now they're diluted down, drifted away, and maybe even selected against to end up 2.9% in me. I think that's about right.

These findings, that many people like me with ancestry from the northern hemisphere share small percentages of their DNA with Neanderthals, are not at all surprising to me. And that's for a couple reasons having to do with what we know about Neanderthals at this moment in scientific history, which in turn has a lot to do with why I titled the post the way that I did, which in turn has to do with my love of Young Frankenstein, and I think it's fairly common to think of Frankensteins and golems in the same imagination space as Neanderthals...

People are still studying Neanderthal feet and limb proportions to try to estimate energy expenditure during locomotion. But since we stopped basing all our reconstructions off an old man with arthritis, and a bunch of badass bone breaks that healed, we've accepted that Neanderthals are not clumsy, knuckle-draggers. They were good bipeds like we are--just coming into dangerously close contact with dinner and surviving well enough to string out their suffering before death.

Whether they had language is more of a lingering question but still one that's lop-sided towards yes, with the caveat that it probably wasn't as diverse and therefore wasn't as complex as ours. New research on a Neanderthal hyoid (small horse-shoe shaped bone in our throats that moves when we swallow and speak) claims that its structures reflect speech mechanics. But I really like reading about the work by Lieberman and McCarthy (written about broadly here) that explains how the Neanderthal throat and mouth dimensions probably did not allow for the tongue to move as much as ours does to manipulate expired air. This is how we make different vowels. Lieberman and McCarthy suggest Neanderthals couldn't have made as many distinct vowels as us and probably were as limited as human children in that regard. (Immature throat and mouth dimensions contribute to why kids sound like accented foreigners while they're developing.) Without as many vowel options their vocabulary would have been limited, but not non-existent! Surely they could produce something approximating this, no? Which brings us to...

So if it walks like a human, and sort of talks like a human, it probably bleeps like a human too. And our imaginations needn't feel naughty for going there since I already told you, if the methods are good, I carry evidence in every cell of my body that at least one of my ancestors waited until marriage to lose her virginity to a Neanderthal. (If you do want to feel naughty, read Ken's two recent posts here and especially here.)

***

They're so much like us or we're so much like them that we can't always tell their bones from ours! For a fascinating story on this, see Stephanie Pappas's piece "'Neanderthal' Remains Actually Medieval Human."

And yet you might see the latest news of "Neanderthal fossil indicates incest was common" which is about this article and say, Hey! We're not like those incestuous savages! But ... well.. yes we are. We so are. And remember, we don't exactly have this kind of information from fossils that we welcome under the Homo sapiens umbrella and if we did (or when we do) I can all but guarantee we'll be finding some skeletons in those skeletons' closets too.

Neanderthals even took time away from incest to behave in some other pretty amazingly human ways. Scroll down to the bottom and check out what scientists have discovered about Neanderthal behavior just over the last year in this 2013 roundup by Kate Wong.

So despite the shrinking barrier between us and them, that we continue to call them "Neanderthals," sets them apart from us. It sets them apart from the real, or at least more human-y, Late Stone Age and Upper Paleolithic human hominins who begat us, whoever they are. And there's such a long tradition of differentiating them from us that it's hard to break free of the mold and present their story any other way than cloistered off as just that: "Their" story and one that ended before any of them could write it down. So they must have gone extinct, yo. Poof.

No seriously, which is it? Are they like chimps or dogs to us now, or were they like The French or The Red Sox of their day?

Maybe they're something else that we can't fully understand unless we actually encounter one another. So the best anybody can do is bring them to life from the inanimate material they left behind.

And because this is the best we can do, and because the fascination will always fuel it, the Neanderthal enigma can only intensify with more discoveries. It's so satisfying to say something conclusive at the end.

4 comments:

Obviously the Neanderthal gene flow in my ancestry happened before they disappeared, so just having their genes live on in so many humans is clearly not a case against an extinction story. I rambled long enough in the post already which prevented more discussion like this, but man, this question's difficult isn't it!?

Assuming some Neanderthal/modern-human interbreeding, as the DNA shows, then I start thinking "At what point do the mixed-race offspring of Homo neanderthalis, HN, become enough different from HN to be considered pure H, and thus unable to contribute mate with another crossbreed to produce offspring acceptable as N? And does the lack of "purebred" HNs now mean extinction or evolution?"

The easy assumption (which I've seen elsewhere) is that H. sapiens (HS) males mated with HN females, perhaps after "conquering" a tribe or family of HN, but given the HS proclivity to rebel against convention, some HS females, having listened to dire warnings about the neighbors, decided to find out for themselves. At any rate, you wouldn't be getting 2.9% HN SNPs in modern HS females from one chance encounter.

Years ago, when various spec-fic writers postulated the idea of interbreeding between HS and HN, the idea was not received kindly. In fact, I remember some prominent scientist being quoted as saying, in effect, it never happened, couldn't happen, and there was and could be no evidence it ever happened. Yeah. Right. Then came DNA evidence, a lot of it, and here we are with a lot of HN/HS crosses (obviously fertile ones, too, starting with the earliest...or their SNPs wouldn't be in the the HS.)

So if the HN and HS populations could not only interbreed but produce fertile HN/HS crosses...which the DNA evidence shows they did...what does this do to the concept of species? Any species, not just those two, and especially any species in our branch of biology? Before anyone says categorically that HS can't produce viable fertile offspring with another species...probably better to make the (highly unpopular and loudly proclaimed unethical) experiment. Or just say "We don't know."

I find it amusing (in one of those bitter-taste ways) that HS in Northern European and North American countries was so quick to label sub-Saharan Africans as "anthropoid" and speculate on their similarity to Neanderthals and "primitive" characteristics...when it's we, the northern whites, who have more HN DNA than Africans do.

Thanks for the thoughtful comments Elizabeth. I'm inclined to assume as a null hypothesis of sorts that there was a continuous spectrum of hominin variation back in Neanderthal times just as there is on Earth today and so our labeling them as a separate race and discussing their crosses or mixtures with other races is something I see both as a more complicated hypothesis to test and one that is biased by present, historically-built culture--how we humans like to divvy up and compartmentalize variation and "us" versus "them," which is less about biology than culture and is something I bet the Neanderthals loved to do too!

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